This invention relates to a method for preparing fluorine-containing ethane derivatives corresponding to the formula F.sub.k H.sub.n Cl.sub.3-(k+n) C-CZ.sup.1 Z.sup.2 F, wherein k, n, Z.sup.1 and Z.sup.2 have the meanings described below.
There is an increasing need for environmentally compatible halogenated hydrocarbons. Examples of such hydrocarbons have been found to include the fluorine-containing ethane derivatives which contain at least one hydrogen atom, for instance CF.sub.3 CH.sub.3 (R143a), CF.sub.3 CH.sub.2 Cl (R133a), and especially CF.sub.3 CHCl.sub.2 (R123). However, the corresponding 1-fluoro or 1,1-difluoro compounds are also of interest, for instance the compounds CFCl.sub.2 CHCl.sub.2 or CF.sub.2 ClCHCl.sub.2, which are considered environmentally compatible and which can be used as refrigerants, solvents or propellants.
Industrially, such compounds are prepared by catalyzed halogen-fluorine exchange, particularly by chlorine-fluorine exchange, from correspondingly halogenated derivatives. The halogenated starting compounds used for this are, however, very inert with respect to halogen-fluorine exchange. Particularly for preparing higher fluorinated compounds, drastic process conditions are necessary. Despite such drastic conditions, for instance operation in the gaseous phase, the conversions are usually low. A further drawback of known methods is that the catalysts used, which are often very expensive, do not have a satisfactory life.